I monitored the populations and leaderboards a bit when the new campaign started at Balokdaan PC/EU. It was a sunday afternoon, it took about 45 minutes for all factions to fill the board.

By comparing the population indicators to the leaderboard in five-minute-steps, I came to the conclusion that the maximum is very likely in the range I voted for. Of course I had to make a few assumptions about leaving players or slackers standing around earning zero AP. But I'm pretty certain the cap is close to 100/faction (as many have estimated before).

There are regularly 3-4 large PVP guilds active at one time, lets say its 3 - 24 x 3 = 72
Add in the full PUG group of 24 = 96
Add in a couple of 8 man teams = 112
Then 30 soloers = 142
Then 3 x 4 person teams playing at resources = 154
Personally I presume atm the cap for each faction is around 150-175